Such a printer is described in U.S. Pat. No. 4,679,500. When using the printer, the printing types which are disposed at a predetermined printing position are inked and then brought into contact with the medium to be printed. The display or indicating types are associated in their position with the printing types on the belts in such a manner that for each printing type which happens to be disposed in the printing position a corresponding indicating type is disposed in a display position and is visible to the operator so that the operator can see which character, symbol or numeral can be printed with the printing type at that instant in the printing position. For reasons of good legibility the indicating types are generally disposed on a white background. If the setting wheels could be turned with the aid of the setting shaft to any desired extent it could easily happen that the indicating types mistakenly reach the printing position and are inked with printing ink. It would also be possible for printing ink to get onto the background of the indicating types so that the characters, symbols and numerals would then not easily be legible through the display window.
In order to solve this problem, the printer disclosed by the above-mentioned U.S. Pat. No. 4,679,500 uses a stop shoulder which is formed on printing type receivers and to be engaged with a front tooth disposed in adjusting directions of the printing belt as well as a web which is disposed at a location spaced from the stop shoulder for a distance which is smaller than the height of at least the tooth lying in front of each adjustment direction of the printing belt plus the printing belt thickness so that the front tooth is stopped between the stop shoulder and the web so as to stop the printing belt at a predetermined position even when a high torque is transmitted from the actuating knob. The actuating knob is coupled with the setting shaft under frictional forces only and slips on the setting shaft after the printing belt has reached the predetermined position at which the front tooth is brought into contact with the stop shoulder.
When the printing belt has reached the limit position at which it is not adjustable with the aid of the actuating knob by way of the setting wheel, the operator feels a load which is heavier than that felt within the adjustable region, whereby the operator recognizes that the printing belt has reached the limit position. When a desired indicating type happens to pass over the display window in practical use of such a printer, the operator often tries to set the desired indicating type in the display window by turning the actuating knob in the same direction. Such an operation brings about a result that the front tooth passes forcibly through between the stop shoulder and the web, thereby breaking the printing type belt and the web or making the printer itself unusable. Though the actuating knob slips on the setting shaft after the printing belt has reached the limit position at which the printing type belt is not adjustable for preventing the trouble described above, repetition of such a forcible operation results in breakage of the actuating knob or detachment thereof from the setting shaft, thereby making the printer incapable of performing the original function thereof. The conventional printer described above has another defect that it requires a high manufacturing cost since the printer requires special parts such as the web and the web must be set at a precise distance as measured from each of the stop shoulders.
In view of the defects of the conventional printer described above, it is a primary object of the present invention to provide a printer which is structured so that the setting wheel rotates idly when the actuating knob is turned in a direction to advance the printing type belt after it has reached the limit position at which it is not adjustable any longer with the aid of the actuating knob by way of the setting wheel.
Another object of the present invention is to provide a printer which requires no special parts such as the web for stopping the printing belt at a predetermined position, has a simple configuration and can be manufactured as a low cost.